Conventional vascular grafts commonly consist of a textile or polymer tube which is implanted into a patient in a major open surgical procedure. grafts which have been implanted endoluminally, that is from within the vessel, consist of grafts which are combined with stents. Such grafts are very time-consuming to produce and this causes particular problems when a bespoke graft is required to be produced at short notice.
Additionally, one of the major problems of existing vascular grafts for endoluminal surgery is that, because of the tortuous bends commonly encountered between the aorta and iliac arteries of patients with aneurysms, there is a tendency for existing tubular grafts to collapse at least partially. This is because, when the tube is curved for any reason, the external diameter of the curve is necessarily longer than the internal, and the excess graft material on the internal diameter of the curve kinks into the lumen, thereby narrowing or even closing it completely. This problem also arises in vascular grafts for repair of, for example, the popliteal artery because of the extreme bending movements which are imparted to this artery during knee flexion.
Furthermore once a graft has been introduced into an artery by the surgeon and located at the correct position, it is necessary to ensure that it is reliably held at such position.
Some devices in use to date are based upon the combination of a stent with a graft, a stent being a relatively rigid metallic cylinder with highly fenestrated walls. This produces a strong implant but one which is relatively inflexible. Some prior graft stents comprise a woven fabric tube which is supported by a series of wire rings which are stitched to the outer or inner surfaces of the implant. Usually these rings are made in the form of a ‘Z’ stent (as with the ZENITH graft manufactured by Cook Inc., or the TALENT graft manufactured by Medtronic Inc.). The ‘Z’ stent, as well as other graft stents, is known to be relatively inflexible and for this reason, graft stents manufactured using such supports are not easily bent around curved vessels. (A frequent complication of arterial disease is the development of highly tortuous vessels through which it is very difficult to pass substantially rigid graft stents.) Moreover the graft stents are difficult to compress axially and this requires that the length of the patient's vessels must be measured accurately so that the selected graft stent is a good fit. Estimating the length of graft stent required to fit a patient can be surprisingly difficult because the presence of the graft stent itself modifies the anatomy of the patient, straightening tortuous vessels and taking unpredictable paths through aneurysmal voids.
Once measured, another problem for the practitioner is to place the graft stent in the same position as was planned; generally the top or proximal end of the implant is deployed first and the rest of the implant follows. If the top is incorrectly placed, then it follows that the bottom of the implant will also be incorrectly placed because the implants cannot be significantly compressed along their axes.
Most graft stents require the inflation of a balloon inside them to expand the graft to fit within the blood vessel although self expanding designs have been recently introduced.
Most existing designs involve the use of a preformed stent which usually involves expensive construction techniques such as laser cutting and plasma welding.
In attaching the preformed stent to the graft, current devices usually involve multiple individual stitches around the stent and attached to the graft. These stitches are necessarily attached by hand in a costly and time consuming process.
A further problem with the current designs, arising from the substantial stent components, is the difficulty in designing bifurcated grafts which can be used at, for instance, the aorto-iliac bifurcation.
A further problem associated with long graft stents, particularly in the arteries of the lower limb, is irritation of the arteries arising from trauma of insertion and the longer term presence of the synthetic material.